Outline of presentation

Transcription

1 Yilgarn 3/MERIWA Project Hydrothermal Alteration Footprints Peter Neumayr1, Steffen G. Hagemann1, John Walshe2, Leo Horn2 1 Centre for Global Metallogeny, UWA 2 CSIRO, Division of Exploration and Mining

2 Outline of presentation Camp-scale geological overview Camp-scale redox variations Deposit-scale alteration variation Paragenetic studies Whole-rock geochemical analyses Magnetite compositions Exploration implications

3 map Geological map of the St. Ives gold camp Cross-section Geochemical traverse Perth Kalgoorlie Kambalda Modified after Watchorn (1998) Geological Overview

4 Geological Overview Cross-section section through Intrepide After Karen Connors (2002)

5 Detailed Gravity Playa Fault Revenge North Orchin Victory Defiance After Ned Stolz, SIG (2002)

6 Camp-scale redox variations Playa Fault Revenge Delta Fault North Orchin Oxidized Magnetite Pyrite Pyrrhotite Reduced Hematite Magnetite Pyrite Arsenopyrite Pyrrhotite Loellingite 0 5 km A B Victory Defiance

7 Geological Overview W E A B PBS PBS SC DFD DFD FP KSL KSL DCB FP DCB X-SECTION KSL?

8 Detailed gravity data: SIG Camp-scale redox variations Camp-scale redox variations Gamma West Fault Mount Blanc Fault Playa Fault Revenge North Orchin Victory Defiance Magnetite Magnetite/Pyrite 0 5 km

9 Camp-scale redox variations Felsic Porphyries - Magnetite Revenge Victory-Defiance kilometres

10 N S PBS Conqueror Foster N DFD KSL KSL Repulse DCB Nautilus DCB DFD KSL DCB Brittania KAM Sirius PBS DCB South Africa PBS PBS BFL CND Boulder Lefroy BFL BFL S KSL DFD DCB DCB Intense Porphyry Intrusions Pyrrhotite Alt. Magnetite Alt. Gold 1km 1000m

11 1 km Empirical background for Te after Eilu and Mikucki (1996) X-section modified after Phung (1997) Dispersion of Te around Revenge LD7114 Geochemical traverse

12 Geochemical traverse 1 km LD70426 Playa LD70449 Playa LD7114 Revenge T effect Poly. (T effect) del 13 C C 350C 300C 250C Fluid composition:18o is +5 and13c is -2 del 18 O Zonation on 13 C and 18 O composition of carbonate

13 Geochemical traverse Different generations of magnetite: epidote-magnetite magnetite Magnetite pre-dates gold Ep bands, qtz-magchpy veins Ep Mag Mag Hbl-bt porphyry

14 redictive ineral iscovery Revenge Gold Mine Ore Pyrite 10 um Hematite Magnetite Redox switches are important for gold ization LD m Geochemical traverse

15 Geochemical traverse Magnetite chemistry LD LD _1 LD LD LD Reduced V2O3/Al2O3=0.05 V2O3/Al2O3=1 Al2O Oxidized V2O3/Al2O3= V2O3

16 Integration Temporal and spatial integration Most magnetite pre-dates gold Minor hematite-magnetite present at the time of gold deposition in the central corridor Oxidized fluids present at the time of gold deposition Regionally magnetite focused around gravity lows Oxidized fluids are spatially, and most likely genetically, related to felsic to intermediate magmatic intrusions Reduced fluids present in domains subjacent to magnetite Gold ization occurs preferentially in zones of greatest redox gradient

17 Translate preliminary results into exploration criteria Exploration criteria

18 Exploration criteria Exploration criteria Shear zones Ox. Fluid conduits Te anomaly Magnetite halo Reduced fluid zones? Gravity Low

19 Exploration criteria Local exploration criteria Po domain Overlay on traditional exploration criteria (e.g., structure) Redox gradient Mag anomalies

20 Major Highlights Project Review 3-4 Dec. 2002, Canberra Major Highlights St. Ives camp is zoned with respect to redox conditions of ore fluid Hydrothermal alteration forms at different times seafloor alteration (epidote) porphyry-related alteration (epidote-magnetite-chalcopyrite) carbonate alteration (regional fault zone) pre-gold dispersed magnetite gold-related alteration (chlorite, biotite, carbonate, feldspar, pyrite) Hydrothermal magnetite rims gravity lows on camp scale and has a strong spatial association with abundant porphyries

21 Major Highlights Project Review 3-4 Dec. 2002, Canberra Major Highlights Zones of gold ization coincide with zones of greatest redox gradients Some faults (e.g., Conqueror) separated reduced from oxidized fluids Reduced fluids are diffused whereas oxidized fluid are highly focussed Pathfinder elements dispersed >100m around lodes Te dispersion marks size of hydrothermal footprint which can be traced to about 3km away from the deposit Methodology currently incorporated in the St. Ives targeting strategy

22 Progress on Y3 Deliverables Mineral- and geochemical database Alteration geochemical plots 50% completed 40% completed Digital maps of alteration footprints Database of magm.-hydroth. history 4D structural-hydrothermal models Microanalytical database of hydrothermal fluids Numerical and chemical models Generic chemical and structural targeting criteria 60% completed Ph.D. project by Mherdad Heydari 50% completed 20% completed commenced 40% completed

23 Y3 / MERIWA Exploration Impact at St Ives A working group established to maximize impact of research results on exploration targeting research team integral part Working group utilising results generated by Y3/MERIWA in exploration targeting Expect drilling of targets identified by working group in 2004

24 Y3 MERIWA Progress Additional PhDs / Post-doc!! Integration of alteration/geochemical data at deposit to district scale Defining the relative / absolute timing of chemical events at district scale Relating chemical events to deformation events Sources of fluids??? radiogenic isotopes

25 Ongoing/Future Research and Exploration Tasks Determine extent of hydrothermal magnetite in other lithologies; specified structures Distinguish different magnetite types using microanalysis Identify reduced and oxidized fluid conduits along fault zones using ogy and whole-rock geochemistry Fingerprint the geochemical characteristics of reduced and oxidized fluids in the different structural corridors Integrated geochemical/structural models with real fluid compositions Construct 3D/4D geochemical and structural model (Pathfinder Elements) Identify exploration targets in 2D/3D Future Work